This disclosure is directed to systems and methods for recalibrating the timing of operation of a bias transfer element in an image forming device. Specifically, the systems and methods are directed to calibrating the timing of forward and reverse biasing in a document processing apparatus.
Bias transfer elements directly support the transfer of a developed toner powder image from a photoconductive member. A bias transfer element is an element that uses electric charge to attract or repel a substance. Bias transfer elements may transfer a developed toner powder image from a photoconductive member by creating a charge that attracts the toner from the photoconductive member onto a substrate. The process of attracting a substance toward the bias transfer element may be referred to as forward biasing. Similarly, the process of repelling a substance from the bias transfer element may be referred to as reverse biasing. Forward and reverse biasing the bias transfer element are examples of activating the bias transfer element. Bias transfer elements may include bias transfer rolls (BTRs) and bias transfer belts (BTBs).
Due to varying electrostatic forces involved with the transfer process, stray toner and debris particles may adhere to the surface of the transfer support member. Consequently, image quality deteriorates. There is a need, therefore, to clean the surface of the transfer support member to prevent degradation of the quality of subsequent copies and/or to prevent toner particles from being fused to, for example, the backside of the final support sheet. Typical cleaning methods include wiping with a brush, a web, a blade, a magnetic brush, or using an airflow, or a combination of these.
In order to deliver a lower unit manufacturing cost and reduce complexity for office and production markets, cleaning implementation for the bias transfer element may include reverse biasing while using the intermediate transfer belt or photoreceptor belt cleaner to remove toner or contamination. Intermediate transfer belts, photoreceptor belts and photoconductive belts in general are examples of “the belt” described throughout the remainder of this application. One problem associated with the use of reverse biasing in conjunction with the belt cleaner is that the use of reverse biasing involves sensitive timing to reverse bias the belt in inter-document zones, i.e. zones of the belt between transfer regions of the belt, which are those areas designated for image transfer. The reverse bias is applied in the inter-document zones to avoid contamination. The timing is critical to effect cleaning while ensuring that the bias transfer element correctly biases in the transfer regions for transfer of an image to a substrate. With advancing technology, the size of these inter-document zone is decreasing and the speed of the belt is increasing. For example, certain current xerographic image forming systems have inter-document zones of less than 40 mm, with photoreceptor belt or drum speeds of 600 mm per second and higher. As the size of the inter-document zone decreases and the speed of the belt increases, the difficulty with precisely timing the forward and reverse biasing of the bias transfer element to accomplish cleaning becomes particularly acute.
The changing of an attribute of the belt, or a substrate on the belt, caused by close proximity between an activated bias transfer element and the belt may be referred to as engagement between the bias transfer element and the belt. For example, engagement between the bias transfer element and the belt may cause a change in an amount of charge or toner on the belt.
Problems associated with the difficulty of precisely timing the forward and reverse biasing of the bias transfer element can be generated from a number of sources. For example, over the life of the image forming device, various mechanical disturbances and other changes due to, for example, normal wear and tear of the machine, may introduce imprecisions and inaccuracies in the timing of activation of forward and reverse biasing. Environmental factors in the vicinity of the image forming device, such as changes in relative humidity and temperature, may separately introduce, or otherwise add to, such imprecisions and inaccuracies in the timing of activation of forward and reverse biasing. Variations in the composition and characteristics of the transfer substrate, such as, for example, noise attributed to paper type, resistivity or flatness, can also introduce or increase errors. The dimensional stability of the various mechanical components of the device, as well as the electrostatic effects of the device, can be adversely affected. As these errors creep into the device's operation, and the timing of forwarding and reverse biasing begins to drift away from nominal, desired or acceptable values, there is a need to correct or compensate for these errors by recalibrating, to a higher level of precision, the timing of activation of forward and reverse biasing.